KR20220018934A - Method for inspecting insulation of a secondary battery - Google Patents

Abstract

Provided is a method for inspecting the insulation of a secondary battery, wherein inspection time can be reduced. The method for inspecting the insulation of a secondary battery (1), wherein the insulation of a secondary battery (1) is evaluated by connecting external direct current power (EP) to the secondary battery (1) having an initial charge (Q0) accumulated therein and using the situation of power current (I) being converged, comprises the step of having a charge (Q) such that the inclination (α(Q)) of a tangent line on a charge-battery voltage curve (CL) for representing the relation between the charge (Q) of the secondary battery (1) and battery voltage (V) is minimized, as a minimal inclination charge (QL) and selecting the initial charge (Q0) from the range (QR2) of the charge (Q) such that the inclination (α(Q)) is equal to or greater than twice the minimal inclination (αL) (α(Q)>=2αL), wherein the inclination (α(QL)) of the tangent line for the minimal inclination charge (QL) is the minimal inclination (αL).

Description

Insulation inspection method of secondary battery

The present invention relates to an insulation inspection method for evaluating the insulation of a battery inside a secondary battery.

In the manufacture of secondary batteries such as lithium ion secondary batteries (hereinafter simply referred to as “battery”), small metal foreign substances such as iron or copper may be mixed in the inside of the electrode body. As a result, a small internal short circuit may occur in the battery. For this reason, the insulation inside a battery may be inspected.

As this insulation inspection method, the following methods are known. That is, an external DC power supply is connected to the previously charged battery to form a test circuit, and an output voltage Vb (Vb = V0) equal to the battery voltage V0 immediately before the test of the battery is continuously applied from the external DC power supply to the battery. so it is approved Then, when the current value Ib(t) of the power source current I flowing through the inspection circuit converges to a substantially constant value, the convergence current value Ibs is detected. Next, when the detected convergence current value Ibs is larger than the predetermined reference current value Ibk (Ibs>Ibk), the battery is judged as a defective product with low insulation properties (small internal short circuit is generated). Moreover, as a prior art which concerns on the insulation inspection method of such a battery, patent documents 1 and 2 are mentioned, for example.

Japanese Patent Laid-Open No. 2019-016558 Japanese Patent Laid-Open No. 2019-113450

However, in the above-described insulation inspection method, since it takes time for the current value Ib(t) of the power supply current I flowing through the inspection circuit to substantially converge, there is a problem that the inspection time is long.

The present invention has been made in view of the current situation, and an object of the present invention is to provide an insulation inspection method for a secondary battery capable of shortening the inspection time.

In one aspect of the present invention for solving the above problems, an external DC power supply is connected to a secondary battery having a predetermined initial charge amount stored therein to configure a test circuit, and the secondary battery In the insulation inspection method of a secondary battery for evaluating the insulation of a battery, the amount of charge at which the slope of the tangent line in the charge amount-battery voltage curve representing the relationship between the amount of charge on the secondary battery and the battery voltage is the minimum is the minimum gradient charge amount, , when the slope of the tangent line in the minimum slope charge amount is the minimum slope, the initial charge amount is selected from within the range of the charge amount in which the slope is at least twice the minimum slope to be.

In the above-described insulation inspection method, the initial charge amount at the time of the insulation inspection is selected from within the range of the charge amount in which the slope is at least twice the minimum slope. For this reason, when considering the local battery capacity (local battery capacity) of the battery, which is the inverse of the slope, the local battery capacity at the time of the insulation inspection (initial charge amount) is higher than the local battery capacity at the minimum gradient charge amount , only the size of 1/2 or less. When the local battery capacity is small, the battery voltage is greatly reduced due to a slight decrease in the amount of electric charge during insulation inspection, and the power supply current is greatly increased. For this reason, compared with the case where the insulation test is performed using the initial charge amount as the minimum gradient charge amount, the convergence time until the power supply current converges can be significantly shortened, and the test time can be significantly shortened.

Further, it is the above-described method for inspecting insulation of a secondary battery, wherein the initial charge amount is selected from within the range of the charge amount in which the slope is three times or more of the minimum slope.

In the above-described insulation inspection method, the initial charge amount is selected from within the range of the charge amount in which the slope is three times or more of the minimum slope. Thereby, the local battery capacity at the time of the insulation test becomes smaller than when the initial charge amount is selected from within the range of the charge amount in which the slope is at least twice the minimum slope, so the convergence time until the power supply current converges can be further shortened, and the inspection time can be further shortened.

In addition, the insulation inspection method of a secondary battery according to any of the above, wherein the initial charge amount is selected from within the range of the charge amount larger than the minimum gradient charge amount.

It has been found that when the initial charge amount is smaller than the minimum gradient charge amount, the power supply current flowing through the test circuit is greatly changed due to a slight change in the battery temperature, compared to the case where the initial charge amount is larger than the minimum gradient charge amount. In contrast, in the above-described insulation inspection method, the initial charge amount is selected from within the range of the amount of charge having the slope at least twice the minimum slope or at least 3 times the minimum slope and greater than the minimum slope charge amount. do. For this reason, while shortening the inspection time, it is possible to prevent a large fluctuation in the power supply current due to a slight fluctuation in the battery temperature.

1 is a perspective view of a battery according to an embodiment.
2 is a flowchart of a battery manufacturing method including the insulation inspection method according to the embodiment.
3 is a graph showing the relationship between the amount of electric charge stored in the battery and the slope of the tangent line in the battery voltage and electric charge-battery voltage curve according to the embodiment;
4 is a circuit diagram of a test circuit in which an external DC power supply is connected to a battery according to the embodiment.
5 is a graph schematically showing the relationship between the duration of application of the output voltage and the current values of the output voltage, battery voltage, and power supply current for batteries of good and defective products.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings. 1 is a perspective view of a secondary battery 1 (hereinafter also simply referred to as “battery 1”) according to the present embodiment. The battery 1 includes a rectangular parallelepiped box-shaped battery case 10, a flat wound electrode body 20 and an electrolyte 15 accommodated therein, and a positive electrode terminal member supported by the battery case 10 ( 30) and the negative electrode terminal member 40 and the like. In this embodiment, a lithium transition metal composite oxide, specifically lithium nickel cobalt manganese oxide, is used as the positive electrode active material, and a carbon material, specifically graphite, is used as the negative electrode active material.

Next, a method for manufacturing the battery 1 including an insulation inspection method for evaluating the insulation properties of the battery 1 will be described (refer to FIGS. 2 to 5 ). First, in "assembly process S1" (refer FIG. 2), the uncharged battery 1 (refer FIG. 1) is assembled.

Next, in the "first charging step S2" (refer to FIG. 2), the assembled battery 1 is charged for the first time. Specifically, using a restraint jig (not shown), the battery 1 is restrained in a compressed state in the battery thickness direction. In this restrained state, it performs from the first charging process S2 to the insulation inspection process S6 mentioned later.

Thereafter, a charging/discharging device (not shown) is connected to the battery 1, and the battery 1 is initially charged to an SOC of 90% by constant current and constant voltage (CCCV) charging at an environmental temperature of 20°C. In the present embodiment, the state in which the maximum amount of charge QF is stored in the battery 1 is SOC 100%. When this first charging is performed up to SOC 100%, Li precipitation is likely to occur during the first charging, and the positive electrode active material is likely to deteriorate in the subsequent high-temperature aging step S3. .

Next, in the "high-temperature aging step S3" (refer to FIG. 2), the battery 1 charged for the first time is left to stand for 6 hours in an open terminal state under an environmental temperature of 63°C, and aged at a high temperature. When this high-temperature aging is performed, the battery voltage V of the battery 1 decreases, and the battery voltage corresponds to about 80% of the SOC.

Next, in "cooling step S4" (refer FIG. 2), the battery 1 is left to stand at an environmental temperature of 20 degreeC, and left-to-stand cooling is carried out, so that the battery temperature is set to 20 degreeC.

Next, in the "charge amount adjustment step S5" (refer to FIG. 2), the battery 1 is charged by constant current and constant voltage (CCCV) charging at an environmental temperature of 20° C., and the charge amount Q stored in the battery 1 is preset Adjust so that it becomes the specified initial charge amount Q0.

Here, a method for selecting this initial charge amount Q0 will be described. If the battery 1 is considered as a capacitor, the relationship V=Q/C is established between the battery voltage V, the battery capacity C, and the charge amount Q accumulated in the battery 1 (the battery voltage V is proportional to the charge amount Q) ) will be. However, in reality, the battery voltage V is not proportional to the charge amount Q, as judged from the charge amount-battery voltage curve CL shown by the solid line in FIG. 3 . That is, as shown by the broken line in FIG. 3 , the slope α(Q)=ΔV/ΔQ of the tangent line in the charge amount-cell voltage curve CL changes according to the magnitude of the charge amount Q. Incidentally, the graph of the slope α(Q) shown in FIG. 3 is a graph obtained by calculating the slope α(Q)=ΔV/ΔQ from the charge amount Q and the battery voltage V obtained for every 1% of the SOC.

Then, consider the local battery capacity Cp(Q)=ΔQ/ΔV, which is the local battery capacity according to the magnitude of the charge quantity Q. Then, since this local battery capacity Cp(Q) is the reciprocal of the slope α(Q) (Cp(Q)=1/α(Q)), the local battery capacity Cp(Q) also changes according to the magnitude of the charge quantity Q. it can be seen that

Therefore, as the insulation inspection step S6 described later is performed with the initial charge amount Q0 at which the local battery capacity Cp(Q) becomes smaller (the slope α(Q) of the reciprocal becomes larger), the battery voltage V decreases due to a slight decrease in the charge amount Q. The power supply current I flowing through the inspection circuit 100 (refer to Fig. 4), which will be described later, greatly increases. Thereby, the convergence time ts until the convergence of the power supply current I can be shortened, and the inspection time can be shortened. Therefore, prior to this, in the charge amount adjustment step S5, as the initial charge amount Q0, an initial charge amount Q0 with a small local battery capacity Cp(Q) and thus a large slope α(Q) is selected.

Specifically, first, in the charge amount-battery voltage curve CL, the charge amount Q (minimum gradient charge amount QL) at which the slope of the tangent line α(Q) is the minimum and the slope of the tangent line at this minimum slope charge amount QL α(QL) ( =αL). In the battery 1 of the present embodiment, as shown in FIG. 3 , the slope α(Q) is a W-shaped curve, and in the range of 0 to Q3 (SOC 0% to SOC 17%), the charge amount Q The more is, the smaller the slope α(Q), and in the range of the charge quantity Q3 to the charge quantity Q5 (SOC 17% to SOC 28%), the more the charge quantity Q, the larger α(Q) becomes, and the charge quantity Q5 to the charge quantity Q7 (SOC 28% to 28%) In the range of SOC 52%), as the amount of charge Q increases, α(Q) decreases. In addition, in this battery 1, the slope α(Q) is the minimum with respect to the charge amount Q3 (SOC 17%), so the minimum slope charge amount QL=Q3.

Next, the initial charge amount Q0 is selected from within the range QR2 of the charge amount Q such that the slope α(Q) is at least twice the minimum slope αL (α(Q)≧2αL). In this embodiment, as shown in Fig. 3, the range QR2 of this charge quantity Q consists of three ranges QR2a, QR2b, QR2c, and the range QR2a is 0≤Q≤Q2 (SOC 0% to SOC 13%) , the range QR2b is Q4≤Q≤Q6 (SOC 23% to SOC 33%), and the range QR2c is Q8≤Q≤QF (SOC 65% to SOC 100%). When the initial electric charge amount Q0 is selected from within this range QR2, the local battery capacity Cp(Q0) in the insulation inspection step S6 is less than 1/2 of the local battery capacity Cp(QL) in the minimum gradient electric charge quantity QL. can be done with Accordingly, in the insulation inspection step S6, the convergence time ts until the power supply current I converges is significantly reduced to 1/2 or less compared to the case where the minimum gradient charge amount QL is the initial charge amount Q0 (Q0 = QL). This can greatly reduce the inspection time.

In the present embodiment, the initial charge quantity Q0 may be selected from within the range QR3 of the charge quantity Q in which the slope α(Q) is three times or more (α(Q)≧3αL) of the minimum slope αL. As shown in Fig. 3, the range QR3 of this charge quantity Q consists of two ranges QR3a and QR3b, the range QR3a is 0≤Q≤Q1 (SOC 0% to SOC 12%), and the range QR3b is Q9≤Q ≤ QF (SOC 78% to SOC 100%). When the initial charge quantity Q0 is selected from within this range QR3, the local battery capacity Cp(Q0) in the insulation inspection step S6 is 1/3 or less of the local battery capacity Cp(QL) in the minimum gradient electric charge quantity QL can be done with Thereby, in the insulation inspection step S6, the convergence time ts until the power supply current I converges can be further shortened, and the inspection time can be further shortened.

Further, the initial charge amount Q0 is defined as the range QR2H (QR2b, QR2c) of the charge amount Q larger than the minimum gradient charge amount QL among the range QR2 of the charge amount Q described above, specifically, Q4≤Q≤Q6 (SOC 23% to SOC 33%) ), Q8≤Q≤QF (SOC 65% to SOC 100%). In addition, the initial charge amount Q0 is selected from the range QR3H (QR3b) of the charge amount Q larger than the minimum gradient charge amount QL, specifically Q9≤Q≤QF (SOC 78% to SOC 100%) among the range QR3 of the above-described charge amount Q also be Accordingly, in the insulation inspection step S6, it is possible to prevent the power supply current I from greatly fluctuating due to a slight fluctuation in the battery temperature.

In the present embodiment, the initial charge amount Q0 may be selected from the range QR3H (QR3b) of the charge amount Q, specifically Q9≤Q≤QF (SOC 78% to SOC 100%) so as to satisfy all the conditions described above. . In this embodiment, specifically, in this charge amount adjustment step S5, the battery 1 was adjusted to SOC of 90%.

Next, "insulation inspection process S6" (refer FIG. 2) is performed. This insulation inspection process S6 is performed at the environmental temperature of 20 degreeC. The insulation inspection step S6 includes a voltage application step S61, a current detection step S62, and an evaluation step S63. First, in the "voltage application step S61", an output voltage Vb (Vb=V0) equal to the battery voltage V0 before inspection is continuously applied from the external DC power supply EP to the battery 1, and the external DC power supply EP is supplied to the battery 1 ), the power supply current I continues to flow (see FIG. 4). That is, the test circuit 100 is configured by connecting the external DC power supply EP to the battery 1 . Specifically, the positive electrode terminal member 30 and the negative electrode terminal member 40 of the battery 1 are brought into contact with a pair of probes P1 and P2 of the external DC power supply EP, respectively.

In the present embodiment, the equivalent circuit shown in FIG. 4 is assumed as the equivalent circuit of the inspection circuit 100 . As an equivalent circuit of the battery 1, it is assumed that the battery resistance Rs is connected in series in a parallel circuit of the battery capacity C and the self-discharge resistance Rp of the battery 1, and the output voltage Vb of the external DC power supply EP is applied to them. do. The battery capacity C is the battery capacity of the battery 1 (battery component 1C), the self-discharge resistance Rp is a resistance mainly generated by an internal short circuit of the battery 1, and the battery resistance Rs is the battery 1 ) is the DC resistance. Further, in the inspection circuit 100 , the wiring resistance Rw is a wiring resistance distributed in the external DC power supply EP and from the external DC power supply EP to the probes P1 and P2 . Further, the contact resistance R1 is the contact resistance between the one probe P1 of the external DC power supply EP and the positive terminal member 30 of the battery 1 , and the contact resistance R2 is the other probe P2 of the external DC power supply EP and the battery It is the contact resistance of the negative electrode terminal member 40 of (1). Then, the sum of the wiring resistance Rw, the contact resistances R1 and R2, and the battery resistance Rs (Re=Rw+R1+R2+Rs) is defined as the series circuit resistance Re of the inspection circuit 100 .

The power supply current I is a current flowing from the external DC power supply EP to the battery 1, and the self-discharge current Ip is a self-discharge current flowing through the battery 1 (battery component 1C) with self-discharge. . In addition, the external DC power supply EP can control the output voltage Vb generated by its own DC power supply EPE variably and with high precision, and has a voltmeter EPV and can measure the battery voltage V(V). Further, the external DC power supply EP has an ammeter EPI, and the current value Ib (μA) of the power supply current I flowing from the external DC power supply EP (DC power supply EPE) to the battery 1 can be measured with high accuracy.

In the voltage application step S61, first, under the condition of the current value Ib = 0, the battery voltage V (the battery voltage V0 before inspection) of the battery 1 is detected by the voltmeter EPV included in the external DC power supply EP. After that, application of the output voltage Vb (Vb=V0) equal to the battery voltage V0 before the test is started to the battery 1 .

After the start of application of the output voltage Vb (after the application duration t=0), in parallel with the voltage application step S61, a “current detection step S62” is performed. That is, the current value Ib(t) of the power source current I flowing through the inspection circuit 100 is detected. In the present embodiment, the current value Ib(t) is detected by the ammeter EPI included in the external DC power supply EP whenever 1 sec of the application duration t elapses.

Here, in Fig. 5, for each of the batteries 1 of good and defective products, the application duration t of the output voltage Vb by the external DC power supply EP, the output voltage Vb, the battery voltage V(t), and the current of the power supply current I An outline of the relationship between the values Ib(t) is shown. As shown in FIG. 5 , in any battery, the battery voltage V(t) gradually decreases from the battery voltage V0 before the test as the application duration time t elapses, and then after the application duration t=convergence time ts, It becomes an almost constant value (convergence cell voltage Vs). However, since the battery voltage V(t) of the defective battery 1 is significantly lower than that of the good battery 1, the convergence battery voltage Vs is also low.

On the other hand, in any of the batteries, the current value Ib(t) gradually increases from 0 (zero) with the lapse of the application duration t, and then after the application duration t = the convergence time ts, a substantially constant value (the convergence current value Ibs ) becomes However, since the current value Ib(t) of the defective battery 1 is greatly increased compared to the defective battery 1, the converging current value Ibs also becomes a large value.

In the present embodiment, the initial charge amount Q0 is selected from the range QR2 (QR2a, QR2b, QR2c) of the charge amount Q satisfying α(Q)≧2αL as described above. Further, the initial charge amount Q0 may be selected from the range QR3 (QR3a, QR3b) of the charge amount Q satisfying α(Q)≧3αL. In this embodiment, specifically, the initial charge amount Q0 corresponding to 90% of SOC is selected. Accordingly, the convergence time ts can be significantly shortened compared to the case where the initial charge amount Q0 = QL. Although detailed experimental results are omitted, the convergence time ts can be made shorter than the case where the initial charge amount Q0 = QL is 1/2 or less, further 1/3 or less, specifically, about 1/4. Therefore, the inspection time required for insulation inspection process S6 (current detection process S62) can be shortened significantly.

Incidentally, in the present embodiment, the initial charge amount Q0 (corresponding to 90% SOC) is selected from the range QR2H of the charge amount Q larger than the minimum gradient charge amount QL among the ranges QR2 of the charge amount Q described above. Further, the initial charge amount Q0 may be selected from the range QR3H of the charge amount Q larger than the minimum gradient charge amount QL among the ranges QR3 of the charge amount Q described above. Thereby, in the insulation inspection process S6 (current detection process S62), it is possible to prevent the power supply current I from fluctuating greatly due to a slight fluctuation in the battery temperature.

Further, when the current detection step S62 is finished, the voltage application from the external DC power supply EP to the battery 1 is stopped, and the voltage application step S61 is also finished. Thereafter, the external DC power supply EP is separated from the battery 1 , and the battery 1 is decompressed by a restraining jig (not shown).

Separately, in the "evaluation step S63", depending on the situation in which the power supply current I flowing through the inspection circuit 100 converges, that is, based on the magnitude of the converged current value Ibs detected in the current detection step S62, the battery 1 ) to evaluate the insulation inside the battery. In the present embodiment, when the convergence current value Ibs is greater than the reference current value Ibk (Ibs>Ibk), the battery 1 is determined to be a defective product with low insulation and an internal short circuit, and the battery 1 is Remove. On the other hand, when the convergence current value Ibs is equal to or less than the reference current value Ibk (Ibs≤Ibk), the battery 1 is judged to be of high insulation quality. After that, another inspection or the like is performed on the non-defective battery 1 . In this way, the battery 1 is completed.

In the above, although this invention was demonstrated based on embodiment, this invention is not limited to embodiment, It is a range which does not deviate from the summary, It goes without saying that it can be changed and applied suitably.

For example, in the embodiment, the insulation test of the battery 1 was performed during the manufacturing process of the battery 1 , but the present invention is not limited thereto. The insulation inspection of the battery 1 can also be performed on the used battery 1 after being mounted on an automobile or the like or placed on the market alone.

Further, in the voltage application step S61 of the embodiment, the output voltage Vb applied from the external DC power supply EP to the battery 1 is made constant (Vb=V0) regardless of the elapse of the application duration time t, but is not limited thereto. . For example, as described in Patent Document 2, the output voltage Vb at the start of voltage application (application duration t=0) is equal to the battery voltage V0 before the test of the battery 1 ( Vb = V0), while increasing the output voltage Vb after the start of application gradually or in a stepwise fashion is also mentioned.

1: secondary battery (battery)
100: check circuit
S5: Charge amount adjustment process
S6: Insulation inspection process
Q: The amount of charge (accumulated in the battery)
Q0: Initial charge
QL: Minimum Gradient Charge
QR2: range (of the amount of charge whose slope is at least twice the minimum slope)
QR2H : Range (larger than the minimum gradient charge amount among the range of charge amount QR2)
QR3: Range (of the amount of charge whose slope is at least 3 times the minimum slope)
QR3H : Range (larger than the minimum gradient charge amount among the range of charge amount QR3)
C: battery capacity
Cp(Q): local cell capacity
CL: charge-cell voltage curve
α(Q) : (tangential) slope
αL: minimum slope
I: power current
Ib(t) : Current value
EP: External DC Power

Claims (3)

The test circuit 100 is configured by connecting an external DC power supply EP to the secondary battery 1 accumulating a predetermined initial charge amount Q0, and the power supply current I flowing through the test circuit 100 converges. In the secondary battery insulation inspection method for evaluating the insulation of the secondary battery 1 depending on the situation,
The charge amount Q at which the slope (α(Q)) of the tangent line in the charge amount-battery voltage curve CL representing the relationship between the charge amount Q and the battery voltage V for the secondary battery 1 is the minimum When is the minimum gradient charge amount QL, and the slope α(QL) of the tangent line in the minimum gradient charge amount QL is the minimum gradient αL,
Selecting the initial charge amount Q0 from within the range QR2 of the charge amount Q such that the slope α(Q) is at least twice the minimum slope αL (α(Q)≥2αL)
Insulation inspection method for secondary batteries. According to claim 1,
Selecting the initial charge amount Q0 from within the range QR3 of the charge amount Q such that the slope α(Q) is three times or more (α(Q)≥3αL) of the minimum slope αL Insulation inspection method for secondary batteries. 3. The method of claim 1 or 2,
An insulation inspection method for a secondary battery in which the initial charge amount Q0 is selected from within a range (QR2H, QR3H) of the charge amount Q greater than the minimum gradient charge amount QL.

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